1. Technical Field
The present invention relates to an electro-optical device including an element substrate with terminals connected to an external circuit board such as a flexible printed circuit board, a method for manufacturing the electro-optical device, and an electronic apparatus including the electro-optical device.
2. Related Art
Among various electro-optical devices, a liquid crystal device includes an element substrate having a plurality of pixels including pixel electrodes; a sealing member; a counter substrate bonded to the element substrate with the sealing member; and a liquid crystal, serving as an electro-optical substance, held in a region surrounded by the sealing member. The element substrate has a first surface on which the pixel electrodes and terminals are arranged. The terminals are connected to a flexible printed circuit board. The element substrate has a second surface opposed to the first surface. The first and second surfaces of the element substrate usually each have an ultra-violet (UV) curable molding member, extending from the element substrate to the flexible printed circuit board, for protecting a connecting portion between the element substrate and the flexible printed circuit board from an external stress.
In order to use the liquid crystal device as a display for use in mobile electronic apparatuses such as mobile phones, the liquid crystal device needs to have low power consumption. The liquid crystal device refreshes to rewrite the data of each pixel for each frame without depending on a displayed image; hence, a driving circuit for driving the pixels and a control circuit for controlling the driving circuit consume electricity.
The following documents disclose a technique in which each pixel includes a static memory circuit storing one bit and is turned on or off depending on the bit stored in the memory circuit: WO 00/8625, Japanese Unexamined Patent Application Publication No. 8-286170, Japanese Unexamined Patent Application Publication No. 2002-278498, and Japanese Unexamined Patent Application Publication No. 2003-122331. In this technique, the driving circuit need not be operated because refresh is not necessary to display a still image. This leads to low power consumption.
In the liquid crystal device, elements of the driving circuit that are arranged outside a pixel region of the element substrate may be damaged by static electricity while the liquid crystal device is in-process or after the liquid crystal device is completed. In order to protect the elements, the liquid crystal device further includes an electrostatic protection circuit, adjacent to a region containing the terminals, including signal lines extending from the terminals. The electrostatic protection circuit has a configuration in which the signal lines are electrically connected to constant potential lines with diode elements disposed therebetween. In the electrostatic protection circuit, the signal lines can be insulated from the constant potential lines with the diode elements. Hence, the following problem cannot occur: a problem in that the liquid crystal device has increased power consumption.
However, the inventors have found that the liquid crystal device including the electrostatic protection circuit has a power consumption greater than that of a liquid crystal device including no electrostatic protection circuit.
The inventors have investigated why the liquid crystal device including the electrostatic protection circuit has a power consumption greater than that of the liquid crystal device including no electrostatic protection circuit. As a result, the inventors have obtained a novel finding below. In order to reinforce the connecting portion between the element substrate and the flexible printed circuit board with the UV-curable molding member, a UV-curable resin composition is provided on the connecting portion and then cured by irradiating the UV-curable resin composition with UV light. In this operation, UV light is incident on the diode elements of the electrostatic protection circuit, whereby current-voltage characteristics of the diode elements are varied. This allows micro-currents to leak from the diode elements. The micro-currents flow between the constant voltage lines and the signal lines. This leads to an increase in power consumption. Such current leakage hardly causes an increase in the power consumption of conventional liquid crystal devices each including a plurality of pixels having no memory elements. However, the leakage of the micro-currents from the diode elements leads to an increase in the power consumption of the liquid crystal device including the electrostatic protection circuit because the pixels of this liquid crystal device each include a memory element and therefore this liquid crystal device has low power consumption.